The present invention relates to power returnable coilable rules of the type which employ a reel or spool within which are wound the power return or recoil spring and the measuring blade, and which are intended to be inserted into a casing to provide the complete assembly.
As will be readily appreciated, power returnable coilable rules are widely employed because of the convenience which they afford to the user in rewinding the tape within the casing. Most recoilable rules now employ a reel or cartridge containing the power return spring and the measuring blade, and frequently such rules enable the purchaser to replace the reels or at least the measuring blade in the event that it is damaged or broken. In such cartridges, there is generally provided a hub or post which is fixed within the casing and in which one end of the spring is engaged. The reel portion of the assembly is then free to rotate thereabout to permit the blade to coil and uncoil as it is withdrawn from the casing or rewound into the casing.
Various structural arrangements have been proposed and utilized for securing the hub or post member in the cartridge or in the final rule assembly. When the spring is prewound and tensioned in the reel prior to insertion in the case, the member to which its inner end is fixed must be non-rotatable relative to the reel but the reel must, after assembly in the casing, be rotatable relative to the casing. Accordingly, some arrangements have involved temporary hubs which are withdrawn; others have used interfitting elements to effect the change in the member (reel or casing) as to which the spring is non-rotatable.
It is an object of the present invention to provide a novel power returnable coilable rule wherein a shiftable hub member is initially non-rotatably engaged with the reel member and thereafter movable axially into engagement with the casing of the rule upon assembly to permit the reel to rotate about the hub and relative to the casing.
It is also an object to provide such a rule in which the several elements may be readily and relatively economically fabricated and thereafter readily assembled into a long lived structure.
Another object is to provide a cartridge for a coilable rule which may be prewound and readily assembled in the casing.
A further object is to provide a simple and relatively trouble-free method for assembling a prewound cartridge into the casing to form a power returnable coilable rule.